- #1
Suraj M
Gold Member
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Homework Statement
$$ \cos(2x) × \cos(\frac x2) - \cos(3x)× \cos (\frac{9}{2} x) = \sin(5x)× \sin \frac {5}{2}x $$
Homework Equations
$$ \cos(x) + \cos(y) = 2 \cos{\frac{x+y}{2}} \cos{\frac{x-y}{2}} $$
$$ \cos(x) - \cos (y) = -2 \sin \frac{x+y}{2} \sin \frac{x-y}{2} $$
The Attempt at a Solution
I don't know how to start, as there are no common angles(2x,x/2,3x...).
How do i start off?
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